Hey Steve,
Good to know you'll be coming into this part of the world :-) I would love to attend some kind of a get-together if time allows.
Some veg*n restaurants to check out:
Angelica's kitchen - great, mid-price veg place in downtown Manhattan
The Organic Grill - everything's organic and vegan, great place - a little on the small side, but worth it.
Caravan of Dreams - right next to the Organic Grill, they have a very good vegan raw menu
Wild Ginger - in the middle of Chinatown, Asian vegan food, GREAT prices. Highly recommended.
Blossom - a more high-class, pricier option in Midtown. Food is great!
Mint - also pricier establishment, it's not strictly veg*n, but I'd say about half of their menu is veg*n. It's high-class Indian food.
I also recommend the above-mentioned V-Spot in Brooklyn's park slope.
As far as what to see, everybody already gave a lot of advice on that, so I'll just throw in my two cents: don't go to Empire State Building, it's overrated and too many people anyway. Instead, go to "Top of the Rock" observation platform on top of Rockfeller center